The invention concerns a technique for starting a motor vehicle on a downhill route. More precisely, the invention concerns a technique for braking a motor vehicle, independently of the driver, when starting from a stopped state on a downhill route.
Systems which regulate a preset speed when a downhill route is driven with a motor vehicle are known. Such systems are generally known by the name Hill Descent Control (HDC), and are often used in off-road vehicles. According to the preset speed of the motor vehicle, the deceleration of a service brake which is operated independently of the driver, and possibly also a drag torque of a drive motor, are exploited to maintain the preset speed. Additionally, for speed regulation some of these systems use sensors to determine the downhill gradient of the route.
WO 01/14186 A1 describes a method for supporting HDC regulation during starting or downhill driving. The technique described in this document includes actuation of a brake system of the vehicle, independently of the driver, on the basis of a detected speed of the vehicle and at least one external parameter which drives the vehicle.
It is a disadvantage of many of these systems that when starting on a downhill route, transient effects of the HDC regulation occur, and the driver and passengers can feel them as unpleasant. HDC systems which activate the brake independently of brake actuation by the driver require a certain time for actuation, to ensure a suitable decelerating torque. In this time, the motor vehicle can already begin to roll, so that starting regulation from the idle state is no longer possible. For the driver, this transition from the idle state to the control range of HDC regulation can give the impression of lack of feedback by the vehicle. Also, some HDC regulators first brake the motor vehicle from this movement back into the idle state, which not every driver understands. Accordingly, it would be desirable to provide an even transition between the idle state and a preset moving state when starting a vehicle on a downhill route.